1. Field of the Invention
The present invention relates to hydraulic machines.
2. Description of the Prior Art
There are many different types of hydraulic machines that can be used to convert mechanical energy into fluid energy and vice versa. Such machines may be used as a pump in which mechanical energy is converted into a flow of fluid or as a motor in which the energy contained in a flow of fluid is converted into mechanical energy. Some of the more sophisticated hydraulic machines are variable capacity machines, particularly those that utilize an inclined plate to convert rotation into an axial displacement of pistons or vice versa
Such machines are commonly referred to as swashplate pumps or motors and have the attribute that they can handle fluid under relatively high pressure and over significant range of flows. A particular advantage of such machines is the ability to adjust the capacity of the machine to compensate for different conditions imposed upon it.
The swashplate machines are, however, relatively complex mechanically with rotating and reciprocating components that must be manufactured to withstand large hydraulic and mechanical forces. These constraints lead to a reduction in the efficiency due to mechanical and hydraulic losses, a reduced control resolution due to the mechanical inefficiencies and the required size and mass of the components and a relatively expensive machine due to the manufacturing complexity.
In use as a variable capacity machine the swashplate is modulated to achieve a desired movement of component of a machine, either a position, rate of movement or applied force.
The movement of the swashplate is usually controlled by a valve supplying fluid to an actuator that acts through a compression spring on the swashplate. Control signals for the valve are generated from a set controller and a feedback, typically provided by a sensed parameter. In its simplest form the feedback may be provided by the operator who simply opens and closes the valve to achieve the desired movement or positioning of the component. More sophisticated controls however sense preselected parameters and provide feedback signals to a valve controller. The valve controller may be mechanical, hydraulic but more usually electronic to offer greater versatility in the control functions to be performed.
Typically the swashplate acts on a plurality of pistons that are slidable within cylinders formed in a barrel. Reciprocation of the pistons induces flow through the cylinders which are connected alternatively to either an inlet port or an outlet port as the barrel rotates. In view of the relative rotation between the barrel and housing, a port plate is utilised to facilitate the transfer from the cylinders to respective ones of the ports in the housing. There is therefore necessarily relative movement between the port plate and either the housing or the barrel and to ensure hydraulic efficiency a seal must be established across this interface. Any misalignment between the barrel and housing will affect the ability to establish an effective seal and accordingly the faces of the port plate are lapped and the barrel typically mounted on a shaft by a splined connection to provide accurate alignment of the barrel. However, such a connection is expensive to manufacture and is susceptible to wear due to the pulsating loads imposed on the barrel as it rotates.
It is therefore an object to the present invention to obviate or mitigate the above disadvantages.